Solar radiation is a prime source of energy, collected by means referred to generally as "insolation", it being a general object of this invention to efficiently capture heat energy from the sun rays by means of optical concentration and fluid media absorption. Solar concentration is of primary concern, it being the heat rays which are to be concentrated at a focal plane with the least loss. The geometric concentration is to be, for example, one hundred to one, whereby 500.degree.-700.degree. F. fluid is produced from the absorber at pressure up to, for example, 700-800 p.s.i.
Heretofore, lens and mirror systems for insolation have been cumbersome and space consuming, and the receivers and absorbers have been wasteful of incoming light. That is, very large areas have been required for solar collection, and there has been dispersion of otherwise useful light ahead of and at the absorber target. It is acknowledged that the objective area is a controlling factor which determines the quantity of light to be collected and subsequently concentrated, and it is this area which is minimized by the present invention by employing a "prism-lens" objective array having a number of advantageous features as hereinafter described. The optical concentration of light provided by the prism-lens array is focused upon a plane within the receiver, entering therein through a narrow slot-shaped window, to be captured within the internally reflective confines of the vacuumized receiver and concentrated onto the absorber, as will be described.
The "prism-lens" array which characterizes the solar light objective area of the present inventive concept is comprised of a multiplicity of linear light concentrators of slat configuration. It is an object of this invention to concentrate light by focusing it upon the absorber plane, utilizing each slat as a lens and for example a convex lens having camber that focuses onto the absorber focal plane. It is the infrared heat rays which have greatest heat value and which are of longer wave length focused upon said absorber focal plane, while the ultraviolet light at the opposite end of the spectrum and of shorter wave length is of less effective heat value and is focused short of said focal plane. In accordance with this invention, it is an object to concentrate the useful solar light and especially the Yellow to Red light, Blue to Violet light being marginally useful. Therefore, the receiver of this invention is characterized by its "slot" window through which the useful solar light is concentrated and focused upon the absorber focal plane. A feature is that each slat is a prism-lens focused upon the absorber focal plane.
The slat prism-lens array as it is disclosed herein is similar to a Fresnel Lens, and accordingly is a weight saving feature. However, this slat prism-lens array must be exposed to the natural environment, namely the wind element of the atmosphere, and it is wind gusts to which the apparatus is subjected and to which it must be structurally resistant. Accordingly, the slat elements of this lens array are spaced for ventilation, but without sacrifice with respect to light collection efficiency, the base of each prism-lens cross section being disposed so as to reflect light through said space and onto the focal plane of the absorber. Note that this spacing increases toward the opposite ends of the array, the array being symmetrical about a central projection plane.
Efficiency of insolation requires minimized attenuation of incoming solar light and reduction of re-radiation. Accordingly, it is an object of this invention to provide an efficient prism-lens array and efficient receiver-absorber combination. Lenses of acrylic are employed for their low (8% per inch thickness) attenuation, and the "slot" window receiver is internally reflective and vacuumized and/or internally insulated.
The "prism-lens and slot absorber" combination of the present invention is a linear apparatus, in that the slats and slot receiver-absorber are elongated for the reception of large quantities of solar light concentrated upon a restricted focal plane area. As shown, the prism-lenses and receiver-absorber are disposed in parallel relation, so that light from the entire area of the slat array is projected through the slot and onto the focal plane target. In practice, the concentration of solar light is within a feasible range of use, for example within the aforesaid range of 500.degree.-700.degree. F., and distributed along the "slot" window and evenly upon the focal plane and absorber elements, whereby common commercially available materials are useable in constructing the receiver and its supporting structure. Only at the focal plane is any of the apparatus subjected to high heat, and only to that structure which is in close proximity to the concentrated light.
Solar tracking is to be considered, it being an object of this invention to simplify tracking with single or a dual axis system responsive to the azimuth and at least the altitude positions of the sun, regardless of the latitude and longitude placement of the apparatus. The slat lens array herein disclosed is particularly adapted to either single or dual axis tracking, it being a simple matter to track each function of the sun's position within the resolution desired, as will be described. Accordingly, there are means that separately determine or detect movement of the sun's azimuth and/or altitude, and which actuate drive motors that position the apparatus within the accuracy required for projection of all incoming solar light through the "slot" window and onto the absorber focal plane within the receiver.